1. Field of the Invention
The invention relates to a method and apparatus for providing a structure on a semiconductor wafer by etching a layer over a substrate.
2. Description of the Related Art
In semiconductor plasma etching applications, a plasma etcher is usually used to transfer a mask pattern into a circuit and line pattern of a desired thin film and/or filmstack (conductors or dielectric insulators) on a wafer. This is achieved by etching away the films (and filmstacks) underneath the mask materials in the opened areas of the mask pattern. This etching reaction may be initiated by the chemically active species and electrically charged particles (ions) generated by generating a plasma from a reactant mixture contained in a vacuum enclosure also referred to as a reactor or process chamber. Additionally, the ions may be also accelerated towards the wafer materials through an electric field created between the gas mixture and the wafer materials, generating a directional removal of the etching materials along the direction of the ion trajectory in a manner referred to as anisotropic etching. At the finish of the etching sequence, the masking materials may be removed by stripping them away, leaving in its place a replica of the lateral pattern of the original intended mask patterns.
It is known to use in inductively coupled plasma device an RF power source that is pulsed or modulated. It is believed that such pulsing allows electron temperature to drop rapidly during the off portion of the pulse, which lowers the average electron temperature. During the RF off period, when the electron temperature drops rapidly, the plasma ion density decreases at a much slower rate, since ions are more massive than electrons and therefore move much slower than electrons. Therefore, this process may significantly lower the average electron temperature, while keeping the average plasma density approximately unchanged. This may reduce electron shading effects, reducing electron damage to semiconductor device features. Such a process may pulse a single RF frequency.